1. Field of Invention
This invention relates to a method and composition for preventing or limiting the attack and infestation of trees by pine bark beetles, by effectively inhibiting the response of the beetles to their aggregation pheromones.
Bark beetles (Coleoptera:Scolytidae) are serious pests of forests throughout the world. Since most life processes such as feeding, mating, egg laying, and larval development occur safely beneath the bark of the host tree, control of the bark beetles is not possible using conventional control strategies, including use of insecticides.
2. Description of the Prior Art
Chemical signals play an important role in the orientation of insects to their host plants and conspecifics [Dickens and Payne, in Handbook of Natural Pesticides: Methods Volume 1, Theory, Practice, and Detection, ed. N. B. Mandava, p. 201 (1985)]. Compounds produced by feeding or calling males or females may attract both sexes as aggregation pheromones, or only the opposite sex as sex attractants. Chemical stimuli from plants may also be attractive to certain insects [Visser, Entomol. Exp. Appl. 20:275 (1976); Visser et al., Entomol. Exp. Appl. 24:538 (1978)]. In addition to the inherent attractancy of pheromones and certain plant odors, host plant odors, which may be unattractive alone, may enhance or synergize the attractancy of pheromones. For example, the aggregation pheromone of the southern pine beetle, Dendroctonus frontalis Zimm., is enhanced by the host monoterpene, .alpha.-pinene, which shows little inherent attractancy in field tests [Renwick et al., Nature 224:1222 (1969); Payne et al., Environ. Entomol. 7:578 (1978)].
Chemical communication by the guild of the southern pine bark beetles including Dendroctonus frontalis Zimm. (the southern pine beetle), Ips avulsus (the four-spined engraver), Ips grandicollis (the five-spined engraver), and Ips calligraphus (the six-spined engraver) is complicated and involves both beetle and host-tree compounds that can function in various behavioral roles [Vite et al., Nature 272:817 (1978); Birch et al., J. Chem. Ecol. 6:395 (1980); Svihra et al. Naturwiss. 67:518 (1980)]. Several investigations have documented the sequence of arrival and competitive interactions among D. frontalis and the three coinhabiting Ips species, and chemical signals have been found to play an important role in their temporal and spatial patterns of arrival on host trees and the intensity of attacks [Dixon et al., J. Ga. Entomol. Soc. 15:378 (1979); Birch et al., in Current Topics in Forest Entomology, ed. W. E. Waters, John Wiley & Sons, New York, p. 135 (1979); Birch et al., J. Chem. Ecol. 6:395 (1980); Svihra et al., ibid.].
Because bark beetles have such a complex chemical communication system, strategies aimed at disrupting this system could provide an effective and environmentally safe technique for control of the beetles and protection of the trees. Previous attempts to prevent or limit the attack and infestation of trees by bark beetles have included efforts to inhibit this communication between the beetles. Several compounds have demonstrated effectiveness in this regard, such as verbenone and endo-brevicomin, which have been identified as inhibitors of the aggregation pheromones of bark beetles. However, the cost of these compounds is high, limiting their use on a practical or large scale.
Green leaf volatiles are six carbon alcohols, aldehydes and their derivatives, e.g., acetates, which are produced by plants as a product of oxidation of surface lipids [Visser et al., J. Chem. Ecol. 5:13 (1979)]. These compounds appear ubiquitously in green plants and are thought to be released in characteristic ratios by different species. The odorous bouquet released from potato plants consists primarily of green leaf volatiles, and it was shown to be attractive to the Colorado beetle, Leptinotarsa decemlineata [Visser, Entomol. Exp. Appl. 20:275 (1976)]. This attractive effect could be masked or diminished by the addition of other green leaf volatiles [Visser et al., Entomol. Exp. Appl. 24:528 (1978)], as well as volatiles emitted from other non-host plant species [Thiery et al., J. Chem. Ecol. 13:1139 (1987)].
Recently, green leaf volatiles were shown to enhance responses of male and female boll weevils to their aggregation pheromone [Dickens, Proc. XVIII Internat. Congr. Entomol. Abstr. 213 (1988); Dickens, Entomol. Exp. Appl. 52:191 (1989)]. Subsequently, pheromone responses of the Mediterranean fruit fly, Ceratitis capitata, and the smaller European elm bark beetle, Scolytus multistriatus, were shown to be enhanced by green leaf volatiles [Dickens et al., Naturwiss. 77:29 (1990)].